Standing beneath the Pantheon’s massive dome, you can almost hear 2,000 years of history echoing off the marble walls.
The Pantheon in Rome was completed around 126 CE under Emperor Hadrian. Its concrete dome is still the world’s largest unreinforced concrete dome, with a central oculus that is the building’s only natural light source. The oculus (latin for "eye") at the center is the only source of natural light. It is open to the elements, so when it rains, it rains inside—the floor is slightly curved to drain the water away.
